In the chemical industry and other process industries using steam for steam jacketed reactors, heat is lost by either a throw away or collecting the condensed water at atmospheric pressure in an uninsulated make-up water tank. It then mixes with room temperature make-up water which is pumped into the boiler as feed water by a feed water pump.
As a result of the above process, part of the steam condensate, which is at higher pressure than atmospheric, flash over into steam due to pressure drop. The flash steam is lost into atmosphere and also the heat it carries. If an open feed water tank is used and condensate pipes are not insulated between the reactor and tank, condensate heat will also leak out into the atmosphere.